Issue #15478: Raising an OSError doesn't decode or encode the filename anymore

Pass the original filename argument to OSError constructor, instead of trying
to encode it to or decode it from the filesystem encoding. This change avoids
an additionnal UnicodeDecodeError on Windows if the filename cannot be decoded
from the filesystem encoding (ANSI code page).

Doc/library/exceptions.rst

@@ -246,6 +246,12 @@ The following exceptions are the exceptions that are usually raised.
       :exc:`VMSError`, :exc:`socket.error`, :exc:`select.error` and
       :exc:`mmap.error` have been merged into :exc:`OSError`.
 
+   .. versionchanged:: 3.4
+
+      The :attr:`filename` attribute is now the original file name passed to
+      the function, instead of the name encoded to or decoded from the
+      filesystem encoding.
+
 
 .. exception:: OverflowError
 

Lib/test/support.py

@@ -647,6 +647,17 @@ elif sys.platform != 'darwin':
         # the byte 0xff. Skip some unicode filename tests.
         pass
 
+# TESTFN_UNDECODABLE is a filename (bytes type) that should *not* be able to be
+# decoded from the filesystem encoding (in strict mode). It can be None if we
+# cannot generate such filename.
+TESTFN_UNDECODABLE = None
+for name in (b'abc\xff', b'\xe7w\xf0'):
+    try:
+        os.fsdecode(name)
+    except UnicodeDecodeErorr:
+        TESTFN_UNDECODABLE = name
+        break
+
 # Save the initial cwd
 SAVEDCWD = os.getcwd()
 

Lib/test/test_os.py

@@ -2046,6 +2046,76 @@ class TermsizeTests(unittest.TestCase):
         self.assertEqual(expected, actual)
 
 
+class OSErrorTests(unittest.TestCase):
+    def setUp(self):
+        class Str(str):
+            pass
+
+        self.filenames = []
+        if support.TESTFN_UNENCODABLE is not None:
+            decoded = support.TESTFN_UNENCODABLE
+        else:
+            decoded = support.TESTFN
+        self.filenames.append(decoded)
+        self.filenames.append(Str(decoded))
+        if support.TESTFN_UNDECODABLE is not None:
+            encoded = support.TESTFN_UNDECODABLE
+        else:
+            encoded = os.fsencode(support.TESTFN)
+        self.filenames.append(encoded)
+        self.filenames.append(memoryview(encoded))
+
+    def test_oserror_filename(self):
+        funcs = [
+            (os.chdir,),
+            (os.chmod, 0o777),
+            (os.chown, 0, 0),
+            (os.lchown, 0, 0),
+            (os.listdir,),
+            (os.lstat,),
+            (os.open, os.O_RDONLY),
+            (os.rename, "dst"),
+            (os.replace, "dst"),
+            (os.rmdir,),
+            (os.stat,),
+            (os.truncate, 0),
+            (os.unlink,),
+        ]
+        if sys.platform == "win32":
+            funcs.extend((
+                (os._getfullpathname,),
+                (os._isdir,),
+            ))
+        if hasattr(os, "chflags"):
+            funcs.extend((
+                (os.chflags, 0),
+                (os.lchflags, 0),
+            ))
+        if hasattr(os, "chroot"):
+            funcs.append((os.chroot,))
+        if hasattr(os, "link"):
+            funcs.append((os.link, "dst"))
+        if hasattr(os, "listxattr"):
+            funcs.extend((
+                (os.listxattr,),
+                (os.getxattr, "user.test"),
+                (os.setxattr, "user.test", b'user'),
+                (os.removexattr, "user.test"),
+            ))
+        if hasattr(os, "lchmod"):
+            funcs.append((os.lchmod, 0o777))
+        if hasattr(os, "readlink"):
+            funcs.append((os.readlink,))
+
+        for func, *func_args in funcs:
+            for name in self.filenames:
+                try:
+                    func(name, *func_args)
+                except FileNotFoundError as err:
+                    self.assertIs(err.filename, name)
+                else:
+                    self.fail("No exception thrown by {}".format(func))
+
 @support.reap_threads
 def test_main():
     support.run_unittest(
@@ -2074,6 +2144,7 @@ def test_main():
         ExtendedAttributeTests,
         Win32DeprecatedBytesAPI,
         TermsizeTests,
+        OSErrorTests,
     )
 
 if __name__ == "__main__":

Modules/_io/fileio.c

@@ -391,12 +391,7 @@ fileio_init(PyObject *oself, PyObject *args, PyObject *kwds)
 
         fd_is_own = 1;
         if (self->fd < 0) {
-#ifdef MS_WINDOWS
-            if (widename != NULL)
-                PyErr_SetFromErrnoWithFilenameObject(PyExc_IOError, nameobj);
-            else
-#endif
-                PyErr_SetFromErrnoWithFilename(PyExc_IOError, name);
+            PyErr_SetFromErrnoWithFilenameObject(PyExc_OSError, nameobj);
             goto error;
         }
     }